Discussion of the Prior Art
This invention relates to a process for the preparation of 2,2-dimethoxypropane. More particularly, it relates to an improved process for the acid-catalyzed reaction of acetone with methanol to form 2,2-dimethoxypropane, and thereafter recovering the product as an azeotrope with one of the reactants, thereby avoiding the costly extraction methods employed by the prior art.
2,2-Dimethoxypropane is a value intermediate for the production of insecticides and fungicides. It is also used as a dehydrating agent for the removal of water from water-sensitive organic reactions. 2,2-Dimethoxypropane is produced by the equilibrium-controlled reaction of acetone with methanol as follows: ##STR1##
This reaction can be catalyzed by either soluble or insoluble strong acids. However, since the equilibrium is favored towards the starting materials, research has dealt with shifting the equilibrium to the 2,2-dimethoxypropane. For example, Lorrette [Chem. Eng. Progr. Symp. Ser. 63, P. 148 (1967)] has used low temperatures and high methanol/acetone feeds to increase the yield of 2,2-dimethoxypropane. His process is encumbered by the use of an uneconomical working temperature of -27.degree. C. He also uses a cost-intensive caustic extraction as part of his separation process.
Allmang and Scheimeir (GDR Pat. No. 2929827, 1981) use a 1/4 molar ratio of methanol/acetone feed designed to produce an azeotropic mixture of acetone and methanol in addition to the 2,2-dimethoxypropane. However, their process suffers from the very low yield of 2,2-dimethoxypropane and subsequent high volumes of methanol/acetone which must be recycled, because in accordance with their recovery methods, a mole ratio of 4 parts of acetone must be used for each part of methanol in order to form said azeotrope.
Finally, the process described in U.S. Pat. No. 4,136,124 uses a dessicant, calcium sulfate, in large amounts to shift the equilibrium by removing the water produced in the reaction. Of course, this means an added cost due to replacement or regeneration of the spent calcium sulfate.
It is, therefore, an object of this invention to provide a process for the preparation and recovery of 2,2-dimethoxypropane which avoids the difficult and costly methods of the prior art.